Polycystic ovarian syndrome (PCOS) is the most common endocrine disorder of reproductive-aged women. Women with PCOS exhibit poor reproductive performance and are at increased risk for endometrial hyperplasia. During the last funding periods, we described specific derangements in the endometrium of women with PCOS, including high levels of androgen receptors (AR), estrogen receptors (ER), and the pi6o coactivators. In this proposal, we are focused mainly on the role of estrogen and epidermal growth factor (EGF) in normal and PCOS endometrium. Estrogen has both positive and negative effects on implantation. Progesterone limits the action of estrogen through down-regulation of ER and up-regulation of enzymes that metabolize estrogen at the time of embryo attachment. Persistent estrogen actions inhibit expression of specific proteins thought to be essential for normal implantation. EGF family proteins, on the other hand, stimulate expression of implantation related proteins. We hypothesize that estrogen, acting through membrane associated pathways, stimulates the action of EGF family ligands. We will study for the first time a novel membrane-bound estrogen receptor, GPRso, in human endometrial epithelium and define the EGF-mediated signaling pathways elicited by estrogen binding to this G-protein coupled receptor. In Aim i. we will identify factors that influence the estrogen response during the menstrual cycle in normal and PCOS endometrium. In Aim 2. we will describe key effects of estrogen on normal and PCOS endometrium by determining the membrane and nuclear receptor mechanisms through which estrogen regulates the expression of estrogen response factors and other target genes. In Aim a. we will dissect the signaling pathways used by estrogen in regulating the early response gene, Cyr6i. Finally, in Aim 4. we will use in vivo and in vitro models to characterize the responsiveness to progesterone and estrogen and determine the functions of epithelial and stromal cells from normal and PCOS endometrium to identify paracrine factors that may underlie the regulatory dysfunction in PCOS. The experiments will utilize molecular analysis of a combination of human endometrial cell lines, primary cultures of human endometrial cells and human tissue explant models to achieve these aims. Understanding normal and abnormal mechanisms of sex steroid action in human endometrium will provide important insights toward the development, of improved infertility treatments and contraceptive approaches.